One of director Howard Hawks’ biggest hits was the acclaimed comedy His Girl Friday. Released in 1940, the movie starred Cary Grant as a gruff New York newspaper editor who will do anything and everything to stop his star reporter, played by Rosalind Russell, from quitting the paper.

The movie was based on a hit Broadway play called The Front Page, which had debuted to rave reviews in 1928. The play had caught the attention of audiences and critics alike thanks to its coarse and incredibly fast-paced dialog—which, in the words of the New York Times, included “some of the baldest profanity and most slatternly jesting that has ever been heard on the public stage.” Hawks understandably left much of the profanity out of his 1940 movie adaptation but kept the snappy pace and quip-heavy dialog mostly intact. If anything, he made it even faster.

Hawks’ screenplay for His Girl Friday ran to more than 190 pages. Given the usual one-minute-per-page rule of Hollywood scripts, under normal circumstances that would have led to a movie more than three hours long. But Hawks’ dialog included countless overlapping and interrupted lines, completed by different characters finishing each other’s sentences or talking over one another.

Hawks also asked his actors to speak much more quickly than they normally would on screen, giving a fast-paced, more conversational feel to the dialog. As a result, his 190-page script came in at a mere 92 minutes on screen.

To increase the pace and jokiness of the script, moreover, Hawks encouraged his stars to ad-lib as much as they wanted on set. This deviation from the lines came naturally to Grant (who had cut his teeth in the fast-paced world of vaudeville theater), but for Rosalind Russell, this improvisatory approach proved a struggle.

As a result, Russell bent Hawks’ rules a little and secretly hired a copywriter from her brother’s advertising firm to write her ad-libs for her in advance. Incredibly, these pre-written asides worked perfectly, and Hawks had no idea that his leading lady was not inventing her witty lines herself until after production was over.